题目

＿＿＿＿time and labour, cartoonists generally draw the hands of their characters with only 3 fingers and a thumb.        A. To save B. Saved C. Saving D. Having saved   答案：A在过滤操作过程中，必须要用到的仪器是：________、________、玻璃棒、铁圈、________等．